1. Field of the Invention
This invention relates to new and useful improvements in gate valves and more particularly to reducing the torque by reducing the drag on the gate and to reducing the erosion on the gate and valve seat sealing surfaces.
2. Description of the Prior Art
Gate valves, particularly through conduit gate valves, which when opened present an unbroken smooth wall conduit for uninterrupted passage of flow therethrough, are widely used because of their desirable flow characteristics. For example, when such valves are in the opened position, the straight through passage, which is provided, offers no more appreciable resistance to fluid flow than an equal length of pipe. Although good flow characteristics are important, an even more important aspect of any valve is its ability to seal.
A major problem attributable to high pressure gate valves is the problem of actuating stem torque. The excessive stem torque is caused when sliding the gate across the seat while sealing pressure. Additionally, while the prior art has long endeavored to solve the problem of the erosion on the gate and the valve seat sealing surfaces, a satisfactory solution has not yet been found. Erosion occurs primarily at the instant the conduit opening of the gate starts to open into the conduit opening of the seat. The full pressure is being throttled through this orifice resulting in very high fluid velocities which generate localized erosion.